ANALYSIS OF FLUG MUTATIONS THAT AFFECT LIGHT-DEPENDENT CONIDIATION INASPERGILLUS-NIDULANS

Conidiation in Aspergillus nidulans is induced by exposure to red ligh t but can also be induced by blue light in certain mutant strains. We have isolated a mutation in the fluG: gene that abolishes responsivene ss to red light but does not affect the response to blue light. It has been shown that the veA1 (velvet) mutation allows conidiation to occu r in the absence of light. We hale identified three other fluG mutatio ns that suppress the veA1 phenotype; these double mutants do not conid iate in the dark. The mutations described here define two new phenotyp ic classes of fluG alleles that display abnormal responses to light. W e have characterized these mutations with respect to their molecular i dentity and to their effect on fluG transcription. Although it has bee n shown that fluG is required for the synthesis of an extracellular fa ctor that directs conidiation, we do not detect this factor under cond itions that promote conidiation in the veA1 suppressors. Furthermore, extracellular rescue is not observed in fluG deletion strains containi ng the wild-type veA allele. We propose that a genetic interaction bet ween fluG and veA influences the production of the extracellular signa l and regulates the initiation of conidiation.